Controllable oscillator tube



' y 9, 1957' H. v. NEHER 2,798,982

CONTROLLABLE C-SCILLATOR TUBE Filed Dec. 11 1945 2 Sheets-Sheet l F|G'.4FIG.5

g INVENTOR HENRY V. NEHER Y ATTORNEY y 9, 1957 H. v. NEHER 2,798,982

CONTROLLABLE OSCILLATOR TUBE Filed Dec. 11, 1945 2 Sheets-Sheet 2 FIG.6

, l6 INVENTOR HENRY V. NEHER BY WM ATTORNEY United States Patent OfiiceCONTROLLABLE OSCILLATOR TUBE Henry Victor Neher, Pasadena, Calif.,assignor, by mesne assignments, to the United States of America asrepresented by the Secretary of the Navy Application December 11, 1945,Serial No. 634,295

16 Claims. (Cl. 315 -533) This invention relates to an electrondischarge device and more particularly, to a low-voltagevelocity-modulated reflex type of oscillator incorporating grids. Theoutput frequency of this oscillator, which is in and above the superhigh frequency (S. H. F.) band of the spectrum as defined andstandardized by the Federal Communications Commission, is adjustable bymeans of an electrical circuit.

Conventional velocity-modulated reflex oscillators operating in andabove the high frequency end of the S. H. F. band employ an electrongun, the emitted electron stream of which is caused to pass throughsmall apertures placed along the axis of radial symmetry of the resonantcavity. It has been determined that for the condition of maximum poweroutput the transit time of the electrons through the region of highfield intensity surrounding the apertures should be approximately equalto one-half the natural period of the resonant cavity. Due to thetendency for the field to diverge if the size of the apertures isincreased, either the apertures must be made small or the electronvelocity must be increased to keep the transit angle approximately equalto 180 electrical degrees. Because of these factors, suchvelocity-modulated reflex oscillators require electrode operatingpotentials of 1800 to 2100 volts and have apertures which are not sosmall as to be difiicult to manfacture uniformly.

Adjustment of the operating frequency over wide limits is usuallyaccomplished by mechanically changing the physical spacing between theapertures in the resonant cavity of such an oscillator, While adjustmentover narrow limits may. be accomplished by variation of the negativepotential diflerence of the reflector with respect to the cathode. Thedegree of frequency variation by the latter means is a direct functionof the electrical losses involved in the frequency-determining impedanceassociated with the oscillator. Thus the operating frequency of anoscillator having low electrical losses in its resonant circuit cannotbe varied over as wide a range by changing the reflector voltage as canthat of an oscillator having high losses.

Coupling of the integral resonant circuit to a transmission line isusually accomplished by means of a singleturn inductor inserted into theelectromagnetic field produced by the resonant circuit, the degree ofcoupling being a function of the position of the inductor relative tothe field. The small physical dimensions of the coupling inductor andthe resonant circuit require the maintenance of extremely smalltolerancesin assembly if oscillators having reasonably uniformcharacteristics are to be obtained.

Disadvantages inherent in conventional oscillators of the type describedare the high operating potentials required, the lack of convenientelectrical means for remotely changing the operating frequency over wideranges, and the difficulty in obtaining an easily reproducible means forcoupling the generated power to an external circuit.

It is an object of this invention to provide a velocity- 2,798,982Patented July 9, 1957 modulated reflex type of oscillator capable ofoperating at super high frequencies and above which uses grids and doesnot require the use of excessively high operating potentials.

It is a further object of this invention to provide a velocity-modulatedreflex type of oscillator, the output frequency of which is controllableover wide ranges by means of an electrical circuit.

It is a still further object of this invention to provide avelocity-modulated reflex type of oscillator in which a means isincorporated whereby the generated power is coupled to an externalcircuit in such a way that small manufacturing tolerances are notprerequisite to the production of oscillators having uniform outputcoupling characteristics.

These and other objects will be more apparent upon consideration of thefollowing description together with the accompanying drawings, in which:

Fig. l is a sectional view of an embodiment of the invention;

Fig. 2 is a plan view of the second grid mounted on a truncated cone;

Fig. 3 is a sectional view along line IIIIII of Fig. 2;

Fig. 4 is a plan view of the third grid on its mounting 8;

Fig. 5 is a sectional view along line V-V of Fig. 4; and,

Fig. 6 is an exploded view of the waveguide assembly, cavity block andchoke.

Specifically, with reference to the embodiment of this invention shownin Fig. 1, the oscillator comprises an electron gun consisting of aheater 10, a cathode 11, and a focussing electrode 12 designed tooperate at the cathode potential. The electron gun assembly is mountedon a mica insulating support 9. The first grid 13 is so positioned inthe electron stream that it produces an additional focussing effect andhelps to increase the uniformity of electron emission over the surfaceof the cathode.

The electron stream is caused to flow through apertures along the axisof radial symmetry of the resonant cavity 15. A plurality ofsubstantially parallel wires forming a grid is placed across eachaperture so that the high-intensity field is confined largely within thespace between the grids. The second grid 14 is mounted on the end of atruncated cone 34, which forms the bottom of the resonant cavity, whilethe third grid 30 is mounted on a flat ring. The procedure for makingthe second grid 14 is as follows:

A one-half inch square sheet of 0.010 inch molybdenum with a 0.250 inchhole in the center is wound with 0.0006 inch diameter tungsten wire witha spacing of 0.0037 inch. A truncated cone 34, as shown in Figs. 2 and3, is formed from 0.005 inch thick low carbon content steel on which a0.001 inch to 0.002 inch thick coating of copper is applied byelectro-deposition. The copper-plated cone is placed on the grid windingin an inverted position, with the tip of the cone resting on thetungsten grid wires and with the one millimeter hole in the tip of thecone coaxial with the 0.250 inch hole in the molybdenum sheet. Theseparts are placed in an oven in this position and heated together in ahydrogen atmosphere until the copper begins to flow, imbedding thetungsten wires in the copper around the edges of the one millimeter holein the tip of the cone. Heating is stopped when the copper starts toflow to prevent surface tension from pulling the copper away from thetip of the cone. The heated parts are allowed to cool until the coppersolidifies and the cone is then separated from the molybdenum plate,breaking ofi the grid wires outside the periphery of the cone tip. Theexcess wires are then either broken off close to the cone tip with finetweezers or removed with a fine abrasive stone. The grid wires are bowedoutward approximately 0.002 inch by inserting into the cone a roundedtool having a tip radius of 0.100 inch.

It is desirable that the cone be fabricated from a steel having a lowcarbon content, such as Swedish iron, since the tungsten wires carbonizeduring heating and become extremely brittle when higher carbon contentsteel is used.

The third grid 30, shown in Figs. 4 and 5, is made as follows:

A sheet of molybdenum 0.005 inch thick is pierced with a number of 0.046inch diameter holes and is then given a 0.0005 inch coating of gold byelectro-deposition. Two such sheets of gold-plated molybdenum are thenclamped together with a-third sheet, which has been coated with aceramic or other material to which gold will not adhere, placed betweenthem. The three sheets, forming a laminated unit, are then wound withtungsten wire having substantially the same diameter and spacing as thatused in forming the second grid and are placed in an oven and heated ina hydrogen atmosphere until the gold fuses, causing the tungsten Wiresto be goldsoldered to the molybdenum sheets. The laminations areseparated with a razor blade and disks concentric with the 0.046 inchdiameter holes are cut with a blanking die. In this manner, a largenumber of grids with mounting rings can be fabricated with but onewinding and heating operation. The grids 30 so formed are bowed by meansof a rounded tool to conform with the profile of the second grid 14.Distortion of the grid wires in this manner insures that when theyexpand due to heating, the wires of both the first and second grids willmove in the same predetermined direction and by the same amount, thusmaintaining a constant separation between the grids.

The performance of the oscillator depends critically upon the positionand shape of the reflector 29. The tilt of the axis of the reflectormust be maintained accurately to within one degree to prevent the phasevariation of the reflected electrons from exceeding 90 electricaldegrees. This precise alignment is accomplished by enclosing thereflector in a steel cylinder 32 and supporting it coaxially with aceramic tube 28, which provides electrical insulation. The steelalignment cylinder is given a coating of silver and copper inapproximately eutectic proportions by electro-deposition.

A ring of nickel wire 26 is spot-welded to the reflector conductor whichpasses through the ceramic tube 28 to fix the reflector 29 in theceramic tube. The proper position of the reflector 29 with respectto'the third grid 30 is maintained by means of ceramic cement 27.

A 0.005 inch thick circular diaphragm 33 of a' copperplated alloy havinga low coefiicient of thermal expansion, such as Kovar, and havingconcentric corrugations to provide axial flexibility, forms the top ofthe resonant cavity 15. The mounting ring containing the third grid 30,the silver-copper-plated reflector alignment cylinder 32 and thecopper-plated Kovar diaphragm 33 are placed in a jig which holds theparts coaxial and spot-welded together. The assembly is then placed inan oven and heated until the silver and copper plating, forming asolder, flows into the cracks and forms a fillet between the diaphragmand the grid ring.

The resonant cavity 15 is formed by a 0.230 inch diameter hole in ablock 16 of copper-plated steel 0.040 inch thick, closed on one end bythe cone 34 holding the second grid 14 and on the other by the diaphragm33 and the third grid 30. One side of the cavity is cut away, as shownin Fig. 6, thus forming an impedance matching transformer 35 between theresonant cavity, and the tapered waveguide transmission line 37. Thedimensions of the impedance matching transformer 35, which is 0.020 inchlong, 0.040 inch high and 0.095 inch wide, are so selected that asatisfactory compromise is eflfected between degree of coupling and thevariation of impedance as a function of frequency.

Two sheets of copper-plated steel, each bent to form a tapered U-shapedchannel as shown in Fig. 6, are fastened to the flat surfaces of thecavity block. One such sheet is held between the cavity block 16 and thediaphragm 33 holding the third grid 30, while the other is mountedbetween the cavity block and the cone 34 holding the second grid 14. Thesheets are spot-welded and silver-soldered together so as to form awaveguide transmission line 37 in the form of a tube having arectangular cross section tapering from inside dimensions of 0.040 inchby 0.410 inch to 0.170 inch by 0.410 inch. Cooling fins 36, formed from0.005 inch thick copper sheet, are fastened to the tapered waveguidetransmission line as shown in Fig. 1 and Fig. 6 to aid in dissipatingthe heat produced in the oscillator. A choke 41 having a circular slotelectrical degrees deep and with the bottom of the slot placedelectrical degrees from the center of the wide edge of the waveguide isfastened to the large end of the tapered waveguide transmission line 37.

The choke .is electrically insulated from and is held in positioncoaxial with a sheet steel envelope 44, which is preferably evacuatedand encloses the complete apparatus shown in Fig. 1, by means of a micaring 43, placed between the envelope and a skirt 38 fastened to thechoke. Power is extracted from the evacuated envelope through a 0.250inch diameter window 39 of low-loss glass having a definite thicknessand being sealed into a cup 40 of metal having the same thermalcoeflicient as the lowloss glass, such as Kovar. The proper thickness ofthe glass window is a function of the dielectric constant of the glassat the operating frequency and may be so selected that the overallreflection coeflicient of the glass window in combination with the chokeis very low, resulting in a voltage standing-wave ratio of approximately1.1 to 1.

A metal collar 42 is fastened to the top structure of the envelope toprovide means for fastening the tube to the external transmission linefittings.

Tuning of the resonant cavity 15 is accomplished by varying the spacingbetween the second grid 14 and the third grid 30. A V-shaped tuningstrut 18, consisting of two Nichrome strips 0.005 inch thick and 0.110inch wide with the central portion stiffened by an embossed ridge, isfastened to the cavity block by means of a yoke 17. The vertex of thestrut is fastened to the reflector alignment tube 32. The upper memberof the strut 18 forms the anode of a triode electron tube 20 having agrid 23 and an indirectly heated cathode 22 held in position by micasupports 21. A decrease in the negative potential difference between thegrid 23 and the cathode 22 causes an increase in space current. Theresulting increase of electron bombardment of the anode causes it toheat and expand. The differential expansion thus produced between thetwo members of the strut causes the reflector alignment cylinder 32 tomove toward the cathode 11. The spacing between the second and thirdgrids, 14 and 30 respectively therefore decreases, causing a decrease inthe frequency of the oscillations. A 0.003 inch thick by 0.100 inch widecopper strip 31 is fastened between the reflector alignment cylinder 32and the cavity block 16 to conduct the heat away from the ends of thestruts 18 and to conduct away the heat caused by intercepted currentflowing in the third grid 30.

The entire inner structure is coated with a colloidal suspension ofcarbon in water after assembly to increase the heat dissipationproperties of the oscillator. The inside of the metal envelope 44 isblackened by oxidation before assembly of the oscillator.

An alternative method of construction, resulting in somewhat betteroperating characteristics, involves the fastening of the inner structureto the envelope by a metal block to permit adequate heat dissipation,and eliminating the blackening process. This is a disadvantage from theoperational standpoint because the envelope must be operated at apotential difference with respect to ground.

a eas? In this case, themetal collar 42 is replaced by one composed ofan insulating'material such as aphenolic resin, thus facilitatingmechanical connection to the external transmission line althoughmaintaining electrical insulation.

The oscillator herein described operates with a potential difference of300 voltsbetween the cathode and the resonant cavity structure and witha reflector potential of less than 150 volts negative with respect tothe cathode. The oscillator is tunable over a 6 percent band offrequencies by means of any suitable electrical circuit controlling thepotential difference between the grid and cathode of the triode 20, thetuning being accomplished in approximately 1.2 seconds.

Since certain changes may be made in the above described article anddifierent embodiments of the invention could be made without departingfrom the scope thereof, it is intended that all matter contained in theabove description or shown in the accompanying drawings shall beinterpreted as illustrative and not in a limiting sense, andparticularly, that dimensions of parts herein described be regarded asillustrative only and therefore, that the invention'is to be limitedonly by the prior art and the spirit of the appended claims.

What is claimed is:

1. An electron discharge device comprising an evacuated envelope, acathode capable of emitting electrons, a focussing electrode for saidelectrons, a first grid of wires spaced from said focussing electrodeand cooperating therewith to form said electrons into an electronstream, 'a cavity resonator having said first and additional second andthird grids so positioned that said electron stream is passed throughsaid grids, a reflector so positioned as to return said electron streamtoward said cavity resonator, an opening in said cavity resonatorforming an impedance-matching transformer, a waveguide transmis sionline having one end electrically connected to said impedance-matchingtransformer and the other end open, a choke surrounding the periphery ofsaid open end of said waveguide transmission line, and a tuning strutincluding members so positioned that linear expansion of one of saidmembers changes the spacing between said second and third grids in saidcavity resonator.

2. The combination of claim 1 with another electron discharge deviceincluding a cathode, grid, and anode, said anode being formed by one ofsaid strut members, the current flow between said cathode and said anodebeing controlled by said grid to control thereby the temperature andthermal expansion of said one member and hence the resonant frequency ofsaid cavity resonator.

3. In an ultra-high frequency reflex velocity-modulated tube oscillator,the combination of an evacuated envelope containing a cavity resonatorhaving parallel apertures, a fine wire grid, a cone shaped frame havingan aperture, means mounting said grid and said frame across saidaperture to form a re-entrant base for said cavity resonator, a flaredwave guide coupled to said cavity resonator within said evacuatedenvelope for transmitting the power generated by said oscillator to anexternal load, and means associated with said cavity resonator forcontrolling the spacing of said apertures of said cavity resonator forcontrolling the frequency of said oscillator.

4. In an ultra-high frequency reflex velocity-modulated tube oscillator,an evacuated envelope, tuning apparatus within [the evacuated envelopecomprising a cavity resonator having parallel apertures, fine wire gridsadapted to be mounted across said apertures, an opening in said cavityresonator forming an impedance-matching transformer, a flared wave guidetransmission line coupled to said impedance-matching transformer fortransmitting the power generated by said oscillator [to an externalload, strut means coupled to said cavity for changing the spacing ofsaid apertures in accordance with temperature variations in said strut'means, and means coupled to said strut means for controlling thetemperature of said strut means to control the frequency of saidoscillator.

5. An electron discharge device comprising an enclosing vessel, aunitary mount assembly within said vessel including a foundation platehaving an aperture therein, a flexible diaphragm assembly having a gridportion, extending over one end of said aperture, a grid assemblyextending over the other end of said aperture, having a grid inalignment with said grid portion, and defining a cavity resonator withsaid diaphragm assembly and the bounding wall of said aperture, anaccelerating grid in alignment with said grid portion, a frame mountingsaid accelerating grid and aflixed to said grid assembly, a cathode andauxiliary electrode mounted from said frame and defining an electron gunwith said accelerating grid and an electronic unit for tuning saidresonator mounted from said foundation plate, and means supporting saidassembly within said vessel.

6. An electron discharge device comprising means defining a cavityresonator, said means including a plate having an aperture therein, afirst metallic member having a grid, secured to said plate and extendingacross one end of said-aperture and a second metallic member having agrid, aifixed to said plate and extending across the other end of saidaperture, an electron gun opposite said second member, a sleeve memberaflixed to and extending from said first metallic member, a repellerelectrode within said sleeve member, and means locating said repellerelectrode within said sleeve member.

7. An electron discharge device comprising, an enclosing vessel having abase, a unitary assembly within said vessel comprising a foundationmember having an aperture therein, means mounted by said member anddefining a cavity resonator with the bounding wall of said aperture,electrode means opposite said aperture, supported from said member anddefining an oscillator unit with said resonator, and rigid support meansaflixed to said assembly and to an inner wall portion of said vesselremoved from said base.

8. An electron discharge device comprising, a plate having an aperturetherein, means including a flexible member at one end of said aperture,defining a cavity resonator with a bounding wall of said aperture,electrode means thereadjacent for energizing said resonator, a supportaffixed to said plate and having an arm, a drive member coupled to saidflexible member for actuating it, strut means supported from said armand coupled to said drive member for displacing the latter to flex saidflexible member, thereby to tune said resonator, in accordance withtemperature variations in said strut means, and means for controllablyheating said strut means comprising electrode means.

9. An electron discharge device comprising, means defininga cavityresonator, said means including a plate having an opening extendingbetween opposite faces thereof, a first member aflixed to one face ofsaid plate, extending across one end of said opening and having a gridportion axially aligned with said opening and a second member aflixed tothe opposed face of said plate, extending across the other end of saidopening and having a grid portion axially aligned with said first gridportion, a cylindrical sleeve extending from said first member andaxially aligned with said first grid portion, a repeller electrodewithin said sleeve, means fitted within said sleeve and positioning saidrepeller electrode in coaxial relation with said first grid portion, andan electron gun opposite said second grid portion.

10. An electron discharge device in accordance with claim 9 comprising asupport mounted from said opposite face of said plate and having acylindrical portion coaxial with said second grid portion and whereinsaid gun includes a cathode having an emissive face opposite said secondgrid portion, and an auxiliary electrode coaxial with said emissiveface, the device comprising also an annular member fitted coaxiallywithin said cylindrical portion and mounting said cathode and saidauxiliary electrode.

11. An electron discharge device comprising an evacuated envelopecontaining a reflex velocity modulated oscillator having a cavityresonator, a Wave guide mounted within said envelope and communicatingwith the interior of said cavity resonator for coupling the powergenerated by said oscillator to a load external to said envelope, andmeans attached to said cavity resonator for altering the configurationof said cavity resonator to control the frequency of said oscillator.

12. In combination, an evacuated envelope containing a reflex velocitymodulated oscillator having as a component thereof a cylindrical cavityresonator with grid structures disposed in a pair of apertures in theopposite parallel end walls of said cavity resonator, said'envelopehaving a window transparent to the propagation of the electromagneticenergy generated by said oscillator, a tapered wave guide coupling thepower generated by said oscillator to said window, and electronic meansattached to said cavity resonator for changing the separation betweensaid grid structures whereby the resonant frequency of oscillation ofsaid cavity resonator is varied.

13. Incombination, an evacuated envelope containing a reflex velocitymodulated high frequency oscillator having as a component thereof acylindrical cavity resonator which has first and second grids disposedin apertures in the opposite parallel end walls thereof, said envelopehaving a window that is transparent to the propagation ofelectromagnetic energy, a tapered wave guide section, the flared end ofsaid wave guide section confronting said window and the throat of saidwave guide communicating with the interior of said cavity resonatorwhereby electromagnetic energy generated by said oscillator istransmitted via said wave guide section and said transparent Window toan external load and an electronically heated tuning structure attachedto said cavity resonator for varying the spacing between said first andsecond grid structures and thereby the resonant frequency of said cavityresonator.

14. In an automatic frequency tuning arrangement for use with a highfrequency, velocity modulated reflex oscillater having first and secondgrid structures disposed in apertures in the opposite parallel end wallsof a cavity resonator, means for regulating the spacing between saidgrid structures and thereby the resonant frequency of oscillation ofsaid cavity resonator comprising, a flexible diaphragm securing a firstone of said grid structures to its adjacent end wall, a repellerelectrode, said electrode being mounted within a cylindrical tube memberone end of which is secured to said flexible diaphragm, whereby saidelectrode is maintained in spaced coaxial alignment with said first gridstructure, a V-shaped tuning strut, the apex of said strut beingattached to said cylindrical tube member and its base being fixed tosaid cavity resonator,

one leg of said V-shaped strut forming the anode of an electron tubewhereby upon electron bombardment of said anode said strut is deformedto cause said first grid and said repeller electrode to move together asa unit to or away from said second grid structure.

15. In an automatic frequency tuning arrangement for use with a highfrequency, velocity modulated reflex oscillator having first and secondgrid structures mounted in relatively small apertures in the oppositeparallel end Walls of a re-entrant cavity resonator, means forregulating the separation between said grid structures comprising, aflexible diaphragm securing a first one of said grids to its adjacentend wall, a repeller electrode, means for maintaining said electrode incoaxial alignment with said first grid structure a predetermineddistance therefrom, said means including a cylindrical tube memberhaving one of its ends secured to said diaphragm, a yoke projecting fromsaid cavity resonator, a V-shaped tuning strut having its apex attachedto said cylindrical tube member and its base attached to said yoke, andmeans for bombarding one leg of said strut with an electron stream ofvariable density so as to heat unequally the leg members of said strutand thereby cause its deformation, whereby said first one of said gridsand said repeller electrode are both deflected with respect to thesecond one of said grids.

16. In an automatic frequency tuning arrangement for use with a highfrequency, velocity modulated reflex oscillator having first and secondgrids mounted in a pair of apertures in the opposite parallel end wallsof a cylindrical cavity resonator, means for regulating the separationbetween said grids comprising, a flexible diaphragm securing a first oneof said grids to its adjacent end wall, a tubular member supported fromsaid diaphragm, a repeller electrode mounted within said tubular memberso as to be maintained in coaxial alignment with the first one of saidgrids a fixed distance apart, a V-shaped tuning strut, the apex of'saidstrut being secured to a Wall portion of said tubular member and thebase of said strut being secured to said cavity resonator, one leg ofsaid strut forming the anode of an electron tube, an evacuated envelope,said envelope having a window transparent to the propagation ofelectromagnetic energy, said cavity resonator being disposed within saidevacuated envelope, and a tapered wave guide section having its flaredend confronting said window and its throat end coupled to an opening cutin the side wall of said cavity resonator.

References Cited in the file of this patent UNITED STATES PATENTS2,359,514 Eitel et al. Oct. 3, 1944 2,372,193 Fisk Mar. 27, 19452,402,119 Beggs June 18, 1946 2,454,306 Clifford et a1 Nov. 23, 19482,494,693 Ekstrand et al. Jan. 17, 1950

